The present invention is generally related to backplane, printed wiring board, and multi-chip module devices and, more particularly, embodiments of the present invention are related to such devices having an optical interconnect layer or layers and methods of fabrication thereof.
In general, waveguides are transmission paths adapted to direct the propagation of electromagnetic waves (e.g., light) in a longitudinal direction, while confining those electromagnetic waves within a certain cross-section. A waveguide is defined, in its simplest form, as a set of two or more materials consisting of a region of high refractive index (referred to hereafter as the core region) surrounded by a region or regions of lower refractive index (referred to hereafter as the cladding region(s)).
Integration of guided-wave optical interconnection at the backplane (BP), printed wiring board (PWB), or multi-chip module (MCM) level of system integration has been achieved through a variety of fabrication techniques, including injection molding (Wiesmann, R., et al., Electron. Lett., 32, 2329; Lee, B., et al., IEEE Photon. Technol. Lett., 12, 62), hot embossing (Schroder, H., et al., IEEE Conference on Polymers and Adhesives in Microelectronics and Photonics, October 2001, 337; Mederer, F., et al. IEEE Photon. Technol. Lett., 13, 1032), trench-fill and patterning (Schmieder, K., et al., IEEE Electronic Components and Technology Conference, May 2000, 749), photodefinition (Liu, Y. S., et al., IEEE Electronic Components and Technology Conference, May 1998, 999), and lamination (Liu, Y. S., et al.). Prior technologies, however, rely on the relative index difference available through process-compatible core and cladding materials, which for typical polymers is very small (index contrast  less than 0.03) (Glukh, K., et al., Proc. SPIE Linear, Nonlinear, and Power-limiting Organics, August 2000, 43). As lithographic technology for the BP, PWB, or MCM level approaches the wavelengths of light common to optical interconnect technologies (xcx9c1 xcexcm) (Jain, K., et al., Printed Circuit Fabrication, 24, 24), the importance of increasing the relative index difference between) core and cladding regions increases due to the desire for reduced waveguide-to-waveguide crosstalk and higher optical interconnect densities.
Many methods of coupling light into BP, PWB, and/or MCM-level waveguides have been investigated, including total internal reflection (TIR) mirrors (U.S. Pat. Nos. 6,343,171, 6,332,050, and 5,263,111; Chen, R. T., et al., Proc. IEEE, 88, 780), surface-relief gratings (U.S. Pat. Nos. 6,215,585, 5,761,350, 5,416,861, and 5,469,518), and plastic assemblies for butt-coupling of optical fibers to waveguides (U.S. Pat. No. 6,226,429 and Barry, T. S., et al., IEEE Trans. Components, Packaging, and Manufacturing Technol-Pt. B, 20, 225), for example.
The selection of waveguide core and cladding materials is limited to those materials where the refractive index of the waveguide cladding material exhibits a lower refractive index than the waveguide core material. Proper selection of materials can increase the relative index contrast between the waveguide core and the waveguide cladding. Two key advantages to a high index contrast waveguide technology include decreased bending loss along bent waveguide paths and reduced cross-talk between adjacent waveguides. Lower bending loss allows for more efficient optical power budgets, while reduced crosstalk enables higher interconnect density and reduced optical power splitter dimensions.
Thus, a heretofore unaddressed need exists in industries employing optical waveguide technology to address the aforementioned deficiencies.
Briefly described, the present invention provides for optical interconnect layers and methods of fabrication thereof. In addition, the optical interconnect layers can be integrated into devices, such as backplane (BP), printed wiring board (PWB), and multi-chip module (MCM) level devices. A representative optical interconnect layer includes a first cladding layer, a second cladding layer, at least one waveguide having a waveguide core and an air-gap cladding layer engaging a portion of the waveguide core, wherein the first cladding layer and the second cladding layer engage the waveguide.
The present invention also involves methods of fabricating optical interconnect layers. A representative method for fabricating an optical interconnect layer includes the following steps: disposing a least one waveguide core on a portion of a first cladding layer; disposing a sacrificial layer onto at least one portion of the first cladding layer and a portion of the waveguide core; disposing a second cladding layer onto the first cladding layer and the sacrificial layer; and removing the sacrificial layer to define an air-gap cladding layer within the first cladding layer and the second cladding layer and engaging a portion of the waveguide core.
Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.